Fix the note preview when adding a note or changing the key/volume/panning

[StopMotionEGames]

This PR contains fixes for #449 and improvements related to the issue.

Earlier, when changing the key, colume or panning of a note by scrolling over it, the sound preview was ignoring the layer's volume and panning.

The intended behavior is when changing these values by scrolling over it, the sound played by the preview has to use the layer's volume and panning.

Overview

Based on the toggle_playing.gml, control_draw.gml now has two variables to store the volume and panning preview values. Before playing the preview, the values are calculated relatively to the volume and panning from the note's layer.

add_block_manual.gml and change_block_manual also calculates the volume and panning relatively to the note's layer before playing the sound.

Now, it's fixed and also works with the option "Use mouse wheel to change the key" and "Use mouse wheel to change the instrument" when hovering a layer with volume or panning changed

[StopMotionEGames]

Maybe the volume/panning preview hovering a layer could be a point of confusion.

As the default behavior is not documented how it should be, feedbacks are welcome.

The video below shows the current stable release (3.11) behavior. The second shows the current behavior in this PR

2026-02-26.01-10-45.mp4

2026-02-26.01-22-57.mp4

Note: I'm scrolling to change key/instrument hovering a layer with default volume and another with changed volume

So, should it be a feature available in the Preferences, or should it simply not exist?

[OctoFlareDev]

I think some people are just used to the current behavior (like me) or prefers louder previews so this should be an option in the preferences